If you receive a 7-bit string, you run the parity checks. The result (called the syndrome) is a binary number from 001 to 111. That number tells you exactly which bit to flip to fix the message.
Why the logarithm? Because information is additive. If you flip two coins, the total surprise is the sum of the individual surprises. The logarithm turns multiplication of probabilities into addition of information. The most famous equation in information theory is Entropy ( H ):
[ H = -\sum_{i=1}^{n} p_i \log_2(p_i) ]
If I tell you something you already know (e.g., "The sun will rise tomorrow"), I have transmitted very little information. If I tell you something shocking (e.g., "The sun did not rise today"), I have transmitted a massive amount of information.
Mathematically, the information content ( h(x) ) of an event ( x ) with probability ( p ) is:
